<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>未定义</title>
        <script>
          //1.声明但没有赋值的变量
          var n;
          console.log(typeof(n));  
          //2.声明但赋值为undefined
          var p = undefined;
          console.log(typeof(p));
          //3.引用对象不存在的属性时  
          var obj = {}; //空对象
          console.log(typeof(obj.password));
        </script>
    </head>
    <body>
    </body>
</html>



